nutrient uptake. Though the rock phosphate was applied after the vermicomposting
process, it was interesting to observe that the combination of the vermicompost and
the rock phosphate showed the best results on grain yield, plant N and P. Compared
to the following treatments, no manure, vermicompost alone, and inorganic P
fertilizer, the rock phosphate-enriched vermicompost resulted in a grain yield
49.5% greater and plant P 93.5% greater compared to the average of all the other
treatments (Kumari and Ushakumari 2002). It would have been interesting to
observe the P mineralization had the RP been incorporated during the
vermicomposting process rather than after, as it was done in this study. Also, the
influence of the vermicompost on the soil properties like heavy metal accumulation
was not evaluated in this study.
Mihreteab et al. (2016) used a compost prepared from grass clippings, palm, olive
and ornamental tree prunings with or without rock phosphate enrichment. It was
noteworthy in this study that the rock phosphate amended compost applied to supply
0.59 g P/kg-compost produced seedlings that were comparable to the substrates
substituted with 1.18 P as rock phosphate per kg compost. These results clearly
demonstrated the apatite mineralization potential of the composting, which could
have even been more if vermicomposting had been done. What is interesting in all
vermicomposting research is that though several researchers have indicated positive
nutrient results following rock phosphate or fly-ash-enriched vermicomposting,
research that could compliment these studies, in terms of actual soil studies, are
still rare. Such a study was performed by Bhattacharya et al. (2012) using a fly
ash-enriched vermicompost on red and lateritic soils over a period of two years.
Unlike the normal belief that fly ash-enriched vermicompost will contribute higher
levels of heavy metals, this study reported slightly changed or even reduce heavy
metal levels in soils in the second year. Such information is encouraging, as it points
to the possibility of using materials like fly ash in organic soil fertility management
systems, though thorough studies that support this possibility are still essential.
Using fly ash as a P source, Mupambwa et al. (2017) used a cow dung–waste
paper vermicompost amended with 33% fly ash as a substitute for pine bark planting
media and evaluated its ornamental horticulture potential. Compared to the pine bark
alone, substitution of the fly ash-based vermicompost between 25% and 50%
resulted in the best marigold germination and flower growth. However, this greenhouse study did not also determine the heavy metal uptake in the ornamental
marigold.
18.8 Organic Hydroponics Powered by Vermicomposts:
Opportunities and Challenges
In the face of climate change, most regions have seen erratic rainfall patterns which
have greatly affected crop production, especially within the resource-poor subsistence farmers. One technology that is being promoted as a solution to improve crop
320
H. A. Mupambwa et al.
process, it was interesting to observe that the combination of the vermicompost and
the rock phosphate showed the best results on grain yield, plant N and P. Compared
to the following treatments, no manure, vermicompost alone, and inorganic P
fertilizer, the rock phosphate-enriched vermicompost resulted in a grain yield
49.5% greater and plant P 93.5% greater compared to the average of all the other
treatments (Kumari and Ushakumari 2002). It would have been interesting to
observe the P mineralization had the RP been incorporated during the
vermicomposting process rather than after, as it was done in this study. Also, the
influence of the vermicompost on the soil properties like heavy metal accumulation
was not evaluated in this study.
Mihreteab et al. (2016) used a compost prepared from grass clippings, palm, olive
and ornamental tree prunings with or without rock phosphate enrichment. It was
noteworthy in this study that the rock phosphate amended compost applied to supply
0.59 g P/kg-compost produced seedlings that were comparable to the substrates
substituted with 1.18 P as rock phosphate per kg compost. These results clearly
demonstrated the apatite mineralization potential of the composting, which could
have even been more if vermicomposting had been done. What is interesting in all
vermicomposting research is that though several researchers have indicated positive
nutrient results following rock phosphate or fly-ash-enriched vermicomposting,
research that could compliment these studies, in terms of actual soil studies, are
still rare. Such a study was performed by Bhattacharya et al. (2012) using a fly
ash-enriched vermicompost on red and lateritic soils over a period of two years.
Unlike the normal belief that fly ash-enriched vermicompost will contribute higher
levels of heavy metals, this study reported slightly changed or even reduce heavy
metal levels in soils in the second year. Such information is encouraging, as it points
to the possibility of using materials like fly ash in organic soil fertility management
systems, though thorough studies that support this possibility are still essential.
Using fly ash as a P source, Mupambwa et al. (2017) used a cow dung–waste
paper vermicompost amended with 33% fly ash as a substitute for pine bark planting
media and evaluated its ornamental horticulture potential. Compared to the pine bark
alone, substitution of the fly ash-based vermicompost between 25% and 50%
resulted in the best marigold germination and flower growth. However, this greenhouse study did not also determine the heavy metal uptake in the ornamental
marigold.
18.8 Organic Hydroponics Powered by Vermicomposts:
Opportunities and Challenges
In the face of climate change, most regions have seen erratic rainfall patterns which
have greatly affected crop production, especially within the resource-poor subsistence farmers. One technology that is being promoted as a solution to improve crop
320
H. A. Mupambwa et al.